1. Field of the Invention
The present invention relates to a cyanohydrination cyclic dipeptide catalyst, and a method of directly preparing or activating the catalysts.
2. Description of the Prior Art
Asymmetric synthesis of R-mandelonitrile by addition of hydrogen cyanide to benzaldehyde in the presence of a synthetic dipeptide catalyst is known in the art, as in Oku, Jun-ichi and Shohei Inoue, J.C.S. Chem. Comm., pages 229-230 (1981), and other Oku publications where cyclo(L-phenylalanyl-L-histidine) containing 1/2 mole of water of crystallization was used. However, it has been found that cyclo(L-phenylalanyl-L-histidine and cyclo(D-phenylalanyl-D-histidine) are not necessarily as satisfactory a catalyst for the preparation of certain S-.alpha.-cyano-alcohols of larger chemical structure, particularly (S)- or (R)-.alpha.-cyano-3-phenoxybenzyl alcohol and ring-substituted derivatives thereof. After encountering difficulty in obtaining high enantiomeric excesses, it was discovered that the high enantiomeric excess in the reaction to prepare (S)- or (R)-.alpha.-cyano-3-phenoxybenzyl alcohols was dependent on a particular physical form of the cyclo(L-phenylalanyl-L-histidine) and cyclo(D-phenylalanyl-D-histidine).